US news network CNBC reported yesterday that China had installed anti-ship cruise missiles and surface-to-air missile systems on three outposts in the South China Sea, citing sources with direct knowledge of US intelligence.

Asked about the report, White House spokeswoman Sarah Huckabee Sanders told a regular news briefing: “We’re well aware of China’s militarisation of the South China Sea.”

“We’ve raised concerns directly with the Chinese about this and there will be near-term and long-term consequences.”

Ms Huckabee Sanders did not say what the consequences might be.

A US official, speaking on condition of anonymity, said US intelligence had seen some signs that China had moved some weapons systems to the Spratly Islands in the past month or so, but offered no details.

CNBC quoted unnamed sources as saying that according to US intelligence assessments, the missiles were moved to Fiery Cross Reef, Subi Reef and Mischief Reef in the Spratly Islands within the past 30 days.

Eric Sayers, a former consultant to the commander of the US Pacific Command, called the missile deployment “a major escalation”.

“When China sees that it can get away with these types of actions with little cost — as they did all through 2015 and 2016 — it only makes it more likely they will keep pressing,” Mr Sayers said.

“China sees its participation in the exercise as a sign of its acceptance among the world’s maritime powers but Beijing should not be allowed to militarise this open maritime domain and still be honoured as a welcomed member of the maritime community.”

Last month, US Admiral Philip Davidson, nominated to head US Pacific Command, said China could use its “forward operating bases” in the South China Sea to challenge the US regional presence and “would easily overwhelm the military forces of any other South China Sea claimants”.